1. Field of the Invention
The present invention concerns an x-ray radiator with a radiator housing by which x-ray radiation originating from a focus can be emitted. The invention also concerns an x-ray device embodying such an x-ray radiator and a housing adjacent to the radiator housing. The invention also concerns a computed tomography apparatus with such an x-ray device.
2. Description of the Prior Art
X-ray radiators, for example in x-ray diagnostic apparatuses such as a computed tomography apparatus, normally have an x-ray tube containing an anode. In the operation of the x-ray tube, an electron beam emitted by a cathode of the x-ray tube strikes (ideally) a point (the focus) on the anode, with x-ray radiation originating from the focus being emitted. As a consequence of thermal influences or movements of the anode plate of the anode due to mechanical tolerances, during the operation of the x-ray tube the focus can be displaced from its ideal position on the anode plate, which leads to an unwanted displacement of the x-ray radiation originating from the focus. In order to be able to counteract this displacement of the focus, a pre-diaphragm having a diaphragm opening is provided in a diaphragm housing positioned downstream from the x-ray radiator. The pre-diaphragm additionally normally exhibits (relative to the diaphragm opening) two smaller slits through which the x-ray radiation can pass. The x-ray radiation pasting through the two slits strikes elements that are sensitive to x-ray radiation, whereby it is registered which region of the elements is charged with x-ray radiation. The real position of the focus on the anode plate can be determined and compared with the desired position of the focus by a computation device using the signals generated by the elements and based on the known interval relationship between the focus, the pre-diaphragm and the elements. If a deviation of the focus has been determined, the focus, for example, can be displaced back into its desired position by influencing the electron beam originating from the cathode. This normally is achieved by a suitable adjustment of the electromagnetic field influencing the electron beam, this electromagnetic field being generated with coils arranged at the x-ray tube. The computed determines the modified coil currents for this purpose.
The design of such an x-ray radiator 1 and an x-ray device 3 having a diaphragm housing 2 is shown in FIG. 1. The x-ray radiator 1 has a focus F from which an x-ray beam S originates and has a coarse pre-diaphragm 5 in addition to a beam window 4. A second pre-diaphragm 6 is provided with slits as well as elements 7 and 8 for determination of the position of the focus F, and together with the actual main diaphragm 10 for shaping the useful x-ray beam is integrated into the diaphragm housing 2. A scatter radiation seal 9 is additionally present between the x-ray radiator 1 and the diaphragm housing 2 for protection from scatter radiation.
A disadvantage is the relatively large space requirement of the arrangement composed of the x-ray radiator and the diaphragm housing. Due to the space requirement of this arrangement, for a computed tomography apparatus it has not been possible to design the patient opening (the opening in which or through which a patient is located or moved during an examination with an x-ray computed tomography apparatus) to be larger in diameter without enlarging the outer diameter of the rotary frame on which the x-ray radiator and the diaphragm housing are arranged.